Graphene, which is in a form of a flat single layer carbon film composed of sp2-bonded carbon atoms, is expected to be used as a base material such as an ultrahigh performance electronic device and a transparent conductive thin film due to its specifically high electrical conductivity and optical transmittance. Heretofore, methods for formation of graphene have been developed, such as a method for peeling from natural graphite, a method for eliminating silicon by a high-temperature heat treatment of silicon carbide, a method for forming graphene on various metal surfaces and the like.
In particular, a method for forming a single to several layers of graphene on a surface of a copper foil by a chemical vapor deposition (CVD) method has recently been developed (Non-Patent Literatures 1 and 2). The technique of depositing graphene using a copper foil as a base material is performed by a thermal CVD technique. In this technique, a methane gas as a raw material gas is thermally decomposed at approximately 1,000° C. to form a single to several layers of graphene on the surface of the copper foil.
The technique using the copper foil as the base material enables synthesis of graphene with satisfactory utilizing characteristics of a surface of copper, as compared with a conventional technique using other metals such as nickel. In contrast, the graphene obtained by the synthesis method using the copper foil as the base material has a crystal size of several tens of μm at most right now. To use graphene as a material in a high-performance electronic device or the like, there is a need for the graphene to have as large a crystal size as possible, and thus the issue is to increase the crystal size.